Typically, a solid ink print head contains a reservoir into which molten ink is fed using a drip feed, or umbilical feed system. The print head also contains an array of jetting elements that are attached to a nozzle plate having an array of apertures through which ink exits to form an image on a print surface. Inside the print head, the ink flows from the reservoir to the jetting elements and nozzle plate through a series of channels or manifolds. These channels or manifolds within the print head are typically formed by a combination of discrete layers that are bonded together to form the overall fluidic structure.
Through the use of heaters, the print head is heated such that the solid ink within the print head melts, or becomes liquid during normal operation. During long periods of idleness, or after powering down, the heaters turn off. The associated cooling of the print head causes the ink within the print head to solidify and shrink. This, in turn, causes air to be introduced into the channels or manifolds within the print head. Upon the subsequent power-up, this air manifests itself as air bubbles within the fluidic structure. For the print head to perform correctly, all or substantially all of this air must be removed from the channels or manifolds internal to the print head.
One should note that the terms ‘printer’ and ‘print head’ apply to any structure or system that produces ink onto a print surface whether part of a printer, a fax machine, a photo printer, etc.
Traditional air removal approaches generate waste ink that the system cannot reclaim or reuse. For example, in one approach, the system transports air bubbles to locations along the channels or manifolds, where they can exit the print head through vent holes that are not part of the nozzle plate. In another approach, the system forces the air through the jetting elements and associated nozzles themselves. In yet another approach, the system forces the air through vents or nozzles within the nozzle plate that are not associated with a jetting element. In each of these approaches, ink trapped between the air bubble and the vent or jetting elements also exits the print head. The printers cannot easily reclaim this ink, and it becomes waste.
With the advent of more stringent energy savings requirements, the printer will be required to power down more frequently than is currently required. Correspondingly, the need for purge cycles to remove air introduced into the print head during power down will also increase. This will contribute to more waste ink, resulting in less efficient print heads, higher user costs and unsatisfied customers.